Here are the best choices for each sentence:

14. Tuan writes more **carefully** with fewer mistakes than the previous term. (B)

15. My father is happy because I got **good** results at school. (B)

16. Peter does better at school because he works **more diligently**. (The closest option provided is **more carefully**). (B)

17. He can do sums more **quickly** and read faster. (A)

18. Jane is not **as intelligent as** her brother. (A)

19. She is a very **hard-working** pupil. She spends most of her time studying. (A)

So the answers are:
14. B
15. B
16. B
17. A
18. A
19. A